Proof testing method and apparatus for optical fibres

ABSTRACT

The invention relates to a proof testing method and a proof testing apparatus for optical fibre where a fibre ( 1 ) is guided to a first pulling device ( 2 ) and further to a second pulling device ( 3 ) and then onto a reel ( 11, 12 ), whereby the pulling devices subject the fibre to a desired amount of tensile strength, as a result of which the fibre breaks if the fibre ( 1 ) strength is insufficient. To achieve a continuous pulling and proof testing process, the fibre end is guided in the case of a fibre break between the first and the second pulling device ( 2, 3 ) by means of a first channel section ( 5 ), which guides the fibre to the second pulling device ( 3 ). After the second pulling device ( 3 ) the fibre end is guided into a second channel section ( 8 ) which is off the normal fibre track and along which the fibre ( 1 ) is guided into a scrap fibre processing system. At a desired moment the fibre ( 1 ) is guided from the second channel section ( 8 ) to the normal track, along which the fibre is guided onto a reel ( 11, 12 ).

[0001] The invention relates to a proof testing method for optical fibrewhere a fibre is guided to a first pulling device and further to asecond pulling device and then onto a reel, whereby the pulling devicessubject the fibre to a desired amount of tensile stress, as a result ofwhich the fibre breaks if the fibre strength is insufficient. Theinvention also relates to a proof testing apparatus for optical fibres.

[0002] In the manufacture of optical fibres, a preform is first producedfrom a desired material and when the fibre is drawn, the preform isheated to soften it. A thin fibre is drawn from one end of the heatedpreform and led to a winding station, where the fibre is wound onto areel. Before winding the fibre is coated with a protective layer andoptionally with a powder so that the fibre can move easily with respectto the elements used to support the optical cable during itsmanufacture.

[0003] Fibre production also includes a testing phase to ensure that thefibres meet the requirements set on them by cable production. One of themost important tests conducted on fibres is the proof test, also knownas a pulling test. The purpose of the proof test is to ensure that thefibre sustains the tensile stress to which is may be subjected duringcable production or cable installation. The proof test is conducted e.g.by simply pulling the fibre during its manufacture with a pullingdevice, which applies a predetermined amount of tensile stress to thefibre as it passes through the pulling device. If the fibre is too weak,it breaks.

[0004] Prior art solutions are described e.g. in U.S. Pat. No. 4,601,208and in JP publication 6129967.

[0005] A disadvantage of the prior art solutions is that they are hardto include in a continuous fibre manufacturing process because it hasbeen difficult to continue the process after a fibre break withoutinterfering with the pulling process.

[0006] The object of the invention is to provide a method and anapparatus which eliminate the disadvantages associated with the priorart. This is achieved with a method and apparatus according to theinvention. The method of the invention is characterized in that in thecase of a fibre break the fibre end is guided between the first and thesecond pulling device by means of a first channel section, which guidesthe fibre to the second pulling device, and that after the secondpulling device the fibre end is guided to a second channel section whichis off the normal fibre track and along which the fibre is guided into ascrap fibre processing system, and that at a desired moment the fibre isguided from the second channel section to the normal track, along whichthe fibre is guided onto a reel. The apparatus of the invention ischaracterized in that the apparatus comprises a first channel sectionwhich in the case of a fibre break is arranged to guide the fibre endbetween the first and the second pulling device to the second pullingdevice, a second channel section which is after the second pullingdevice off the normal fibre track and arranged to guide the fibre into ascrap fibre processing system, and transfer means which are arranged toguide the fibre at a desired moment from the second channel section tothe normal track, which is arranged to guide the fibre onto a reel.

[0007] A major advantage of the solution according to the invention isthat it allows combining of the proof testing with the fibre pullingprocess in an advantageous manner so that the fibre pulling process isnot interfered with in any situation but can continue withoutinterruptions at the maximal production rate. The reason for this isthat the invention enables changeover of winding from one reel toanother in an automatic double spooler even though fibre or a similarmaterial to be wound would have broken or intentionally cut before thechangeover of winding. A further advantage of the invention is that itallows winding of proof-tested fibre with a desired length onto a reel.

[0008] The invention will be described in greater detail by means ofpreferred embodiments shown in the accompanying drawing, in which

[0009]FIG. 1 schematically illustrates a first embodiment of theapparatus according to the invention,

[0010]FIG. 2 illustrates the embodiment of FIG. 1 from anotherdirection,

[0011]FIG. 3 schematically illustrates a second embodiment of theapparatus according to the invention,

[0012]FIG. 4 illustrates the embodiment of FIG. 3 from anotherdirection,

[0013]FIG. 5 schematically illustrates a third embodiment of theapparatus according to the invention,

[0014]FIG. 6 is a cross-sectional view of a detail of the embodimentshown in FIG. 5,

[0015]FIG. 7 is a cross-sectional view of another detail of theembodiment shown in FIG. 5, and

[0016]FIG. 8 is a perspective view of the embodiment of FIG. 5 fromwhich part of the structure has been omitted for the sake of clarity.

[0017]FIGS. 1 and 2 schematically show a first embodiment of theapparatus according to the invention. In the figures reference number 1denotes an optical fibre which enters the apparatus from a fibre pullingprocess. The fibre 1 direction is marked with an arrow in FIG. 1.Reference numbers 2 and 3 denote a first pulling device and a secondpulling device. In the embodiment according to FIGS. 1 and 2 the firstpulling device 2 is supported by guides so that the whole unit can movefreely in the longitudinal direction of the fibre 1. However, the firstpulling device 2 is pre-tightened against a power sensor 4 duringinstallation, and thus in practice this unit is fixed. The idea of thisembodiment is that in proof testing the fibre 1 pulls the whole unitforming the first pulling device 1 against the sensor 4, which thenmeasures the tensile stress.

[0018] According to the invention, a first channel section 5, which inthe embodiment shown in FIGS. 1 and 2 is made of a solid tubular member,is arranged between the first pulling device 2 and the second pullingdevice 3. If necessary, an ionised airflow can be led into the firstchannel section. In the case of a fibre break the first channel section5 guides the fibre end into the opening of the second pulling device.The ends of the first channel section 5 are preferably shaped so thatthe fibre I cannot escape from between the end of the channel sectionand the second pulling device 3. The front end of the first channelsection 5 can be provided with a cutter 6, which can be used for cuttingthe fibre 1 intentionally.

[0019] After the second pulling device 3 in the fibre 1 direction theapparatus comprises a unit which is provided with a dancer unit 7functioning as fibre transfer means, a second channel section 8 andauxiliary wheels 9 and 10. During a normal run, the fibre moves frombetween the second pulling device 3 and the end of the second channelsection 8 to the wheel of the dancer unit 7 and further onto a reel viathe auxiliary wheel 9, or onto another reel 12 via the second auxiliarywheel 10, depending on the position of the dancer unit 7.

[0020] In the embodiment of FIGS. 1 and 2 the second channel section 8is formed from an openable tubular section, which splits into two halvesmarked with reference numbers 8 a and 8 b in FIG. 2. The second channelsection 8 can be opened and closed by means of a suitable openingmechanism 13. During a normal run the second channel section 8 isclosed, i.e. the halves 8 a and 8 b are against each other. Ifnecessary, an ionised airflow can also be led into the second channelsection 8.

[0021] As the fibre 1 breaks, its tail naturally travels onto the reel11 via the dancer unit 7, for example. In this case the new fibre 1 endis guided inside the second channel section 8 and along it furthertowards a fibre gripping unit 14 and a suction device 15. From thesuction device the fibre can be led into a scrap fibre processingsystem, for example. After the gripping unit 14 has caught the fibre 1and winding has started, the second channel section 8 is opened and thewheel in the dancer unit moves to the other side of the channel section,taking the fibre to an auxiliary wheel on the same side and windingcontinues onto a reel 12 different from the one used before the break.Finally, the halves 8 a and 8 b of the second channel section 8 arepressed back together and the second channel section 8, which now is atubular channel, remains waiting for a new fibre break. It should benoted that the fibre break may result from weakness of the fibre or canbe caused by a cutter 6. The fibre is broken by the cutter 6 e.g. whenfibres with the delivery length are run onto reels in a process whichcombines pulling and proof testing.

[0022] In the embodiment illustrated in FIGS. 1 and 2 the suction device15 is arranged directly below the second channel section 8 so that thegripping unit 14 fits between them. When the gripping unit closes, acutter 16 at its lower edge cuts off the fibre end towards the suctiondevice. After the second channel section 8 has been opened and the fibreguided to the dancer unit, the spooler transfers it into the windingstation. The reel in the second spooler is replaced with an empty reel,after which it can be transferred below the second channel section towait for a fibre break. If there are a lot of fibre breaks, theclippings are usually led directly into the suction device 15.

[0023]FIGS. 3 and 4 illustrate a second embodiment of the apparatusaccording to the invention. The embodiment shown in FIGS. 3 and 4corresponds to that of FIGS. 1 and 2 in several respects, and thus inFIGS. 3 and 4 the same reference numbers have the same significance asin FIGS. 1 and 2. FIG. 3 schematically illustrates an electricconnection established between the first and the second pulling device 2and 3. The electric connection is used to apply a desired amount oftensile stress to the fibre 1.

[0024] In the embodiment of FIGS. 3 and 4 the pulling devices 2 and 3,first channel section 5, dancer unit 7, auxiliary wheels 9 and 10, andsecond channel section 8 are arranged in the same way as in FIGS. 1 and2. The embodiment of FIGS. 3 and 4 differs from that of FIGS. 1 and 2 inthat in the former embodiment, there is a third pulling device, i.e. anauxiliary pulling device 17, and a second dancer unit 18 functioning assecond fibre transfer means after the second channel section 8.

[0025] In principle, the function of the embodiment according to FIGS. 3and 4 corresponds to that of the embodiment shown in FIGS. 1 and 2. In anormal situation the fibre travels in the embodiment illustrated inFIGS. 3 and 4 via the dancer unit 7 and the auxiliary wheel 9, forexample, onto the reel 11. In the case of a fibre break the new fibreend travels via the first channel section 5 to the second pulling deviceand further to the auxiliary pulling device 17 along the second channelsection. When the fibre 1 is attached to the auxiliary pulling device17, the second channel section 8 is opened, and thus the second dancerunit 18 turns into the position shown with broken lines in FIG. 3,transferring the fibre close to the second reel 12, in which case thegripping unit can catch the fibre. Then the cutter 16 cuts it andwinding continues onto the reel 12 as described above in connection withFIGS. 1 and 2. At the same time the dancer unit 7 transfers the fibre tothe auxiliary wheel 10. Finally, the second channel section closes andremains waiting for a new fibre break. In this embodiment a dischargechannel 19 leading to the suction device 15 is arranged after theauxiliary pulling device 17. The discharge channel can also be providedwith a shredder which cuts the fibre to be disposed of.

[0026] FIGS. 5 to 8 illustrate a third embodiment of the invention. InFIGS. 5 to 8 the same reference numbers have the same significance as inFIGS. 1 to 4. In essence, the embodiment shown in FIGS. 5 to 8corresponds to the embodiments described above; only some details areimplemented differently from the preceding embodiments. In theembodiment shown in FIGS. 5 to 8 the first channel section 5 is formedusing belts and pulleys and the second channel section 8 by means of twoplate members that are arranged close to each other.

[0027] In the embodiment according to FIGS. 5 to 8 the tension relatedto the proof testing of fibre is generated by means of the rate and/ortension control of the first pulling device 2 and the second pullingdevice 3. Since one has to be able to manage the movements of the fibreend in the case of a fibre break, too, a tension measuring wheel cannotbe used for tension measurement between the pulling devices. The forcegenerated by the fibre in respect of the second pulling device can bemeasured e.g. by connecting the second pulling device 3 and its belts tosuitable power sensors.

[0028] One feasible solution for controlling tension is a control wherethe first pulling device 2 functions as the master of line speed,rotating at a constant rate, or in the case of a drawing tower, as apulling device that determines the pulling rate. In that case the secondpulling device 3 is driven by a tension control controlled by powersensors.

[0029] A fibre break can be noticed e.g. by measuring the speeddifference between the pulling devices 2, 3 with HW counters. By usingpulse sensors in the motors of the pulling devices and by increasing thecounter reading by the pulses of one pulling device and decreasing it bythe pulses of the other one the counter will show the difference inlength that corresponds to the fibre stretch. In connection with a fibrebreak this difference rapidly increases more than normally and the fibrebreak can be noticed. Furthermore, the difference in length resultingfrom the stretch and changes thereof can be utilized in calibrationdiagnostics of the power sensors. Other means for measuring a fibrebreak include the power sensor signal, motor current, etc.

[0030] In the embodiment of FIGS. 5 to 8 the pulleys of the pullingdevices 2 and 3 are arranged so that the pulleys 21, 22 and the belts23, 24 between them travelling in the same direction form a firstchannel section 5, which controls the movements of the fibre 1 during afibre break and when the device is threaded. The first channel section 5formed in the above-mentioned manner is shown in FIG. 6, which shows thechannel section in the fibre 1 direction. By means of a suitableconstruction the length of the first channel section 5 can be made tocover nearly the whole length of the proof testing. Naturally it is alsopossible to use suitable nozzles which ensure that the fibre 1 is guidedbetween the belts, etc. Guides 25, 26 shown in FIG. 6, which ensure thatthe fibre stays between the belts, can also be used between the pulleys21, 22. The dimensions of the channel between the belts should beselected so that the fibre can move freely in the channel, in which casethe tension applied to the fibre is generated only by the capstans ofthe pulling devices.

[0031] In the embodiment of FIGS. 5 to 8 the fibre 1 travels from thesecond pulling device 3 into a mechanism forming transfer means arrangedto transfer the fibre to its normal track, to guide the fibre to thenormal track during a normal run and to the second channel section 8 offfrom the normal fibre track. This mechanism consists of two plate-likemembers 27, 28 arranged against each other and related components.Between the plate-like members there is a narrow air gap, which may bee.g. 3 mm wide. The surfaces of the plate-like members are provided withgrooves, and thus in this embodiment the plate-like members arrangedagainst each other form a round-edged groove, which in this embodimentforms the second channel section 8, which can be seen e.g. in FIGS. 7and 8. It should be noted that FIG. 8 shows only one of the plate-likemembers 28. For the sake of clarity, only a very small part of the otherplate-like member 27 is shown in FIG. 8 since this allows a clearerillustration of the second channel section 8. The diameter of the secondchannel section may be 30 mm, for example. The second channel section 8leads into a suction device 29, which is shown in FIG. 5.

[0032] When the suction device 29 is in use, it first generates anairflow from the front end of the second channel section 8 into thesuction device and secondly an airflow from the sides of the plate-likemembers 27, 28 through the air gap along the whole length of the channelsection first into the channel section and then into the suction device.If the size of the channel section and the air gap between theplate-like members are designed so that they are suitable for eachother, it is possible to control how much of the airflow caused by thesuction device comes into the channel section 8 from the end towards thesecond pulling device and how much of it comes from the air gap.

[0033] The arrangement described above enables use of the airflow causedby the suction device for guiding a fibre 1 that has broken during prooftesting or has been intentionally cut into the suction device. Also inthis embodiment the first channel section 5 can be provided with acutter 30 for cutting the fibre intentionally.

[0034] FIGS. 5 to 8 further describe a construction by means of whichthe fibre can be deflected from the second channel section into the areaof the air gap between the plate-like members 27, 28. This is utilizedduring the changeover and winding. In this embodiment it is alsoessential that even if the fibre had been deflected into the area of theair gap between the plate-like members 27, 28, the second channelsection 8 remains functional without interruptions in case the fibrebreaks during proof testing. This is useful particularly when prooftesting is included in fibre pulling. In that case it may happen thatthe fibre is very weak for some time and several fibre breaks occur oneafter another.

[0035] In this embodiment the fibre transfer means include a transferwheel 31 which is arranged to move in a groove 32 formed by theplate-like members 27, 28, e.g. linearly from one side to the other. Thewidth of the transfer wheel 31 is chosen so that it reliably takes alongthe fibre 1 travelling in the second channel section 8. The transfermeans further comprise an accumulator wheel 33, which moves e.g. along acircular track in the groove 34 from one side to the other. The width ofthe collected wheel 33 is also chosen so that it reliably takes alongthe fibre 1 travelling in the second channel section 8. The transfermeans also comprise fixed control wheels 35 to 38 which are embedded inthe cavities included in the plate-like members 27, 28 so that when thetransfer wheel 31 or the accumulator wheel 33 deflects the fibre fromthe second channel section 8, it is guided reliably and correctly.

[0036] In principle, the embodiment according to FIGS. 5 to 8 functionsas follows. It is assumed that in the initial situation the fibretravels along the second channel section 8 into the suction device, e.g.when the run starts. When winding is to be started, the transfer wheel31 moves across the second channel section 8 to the opposite side,deflecting the fibre 1 so that it travels from the transfer wheel intothe suction device along a track which guides the fibre between thegripping flange of the gripping mechanism. The principles of thegripping mechanism were described in connection with FIGS. 1 to 4.Immediately before the gripping flange is activated, the accumulatorwheel 33 also moves to the same edge as the transfer wheel and windingof the fibre onto the reel 11 begins as shown in FIG. 8.

[0037] If the fibre breaks after the phase described above during theproof testing, the airflow generated by the suction device 29 takes thefree end of the fibre along the second channel section 8 into thesuction device, after which changeover of winding onto a new reel can beperformed at a desired moment as described above, i.e. by moving thetransfer wheel 31 and the accumulator wheel 33 to the opposite side,i.e. to the side of the new reel.

[0038] If the fibre 1 is still weak when it is guided between thegripping flanges of the gripping mechanism, this will cause no problemsbecause the second channel section 8 is ready to function all the timeand takes any broken fibres into the suction device. Since thechangeover is a critical point in respect of the fibre strength, theabove-mentioned fact significantly improves the reliability of theapparatus.

[0039] If the fibre should be transferable onto a new reel at anydesired moment, the apparatus must include a fibre cutter for cuttingthe fibre. In the embodiment of FIGS. 5 to 8 a fibre cutter 30 isarranged between a construction comprising the second pulling device 3and the plate-like members 27, 28. After the fibre has been cut by thecutter 30, it is guided onto a new reel as described above. The fibrecutter can be used also when the accumulator wheel and/or the transferwheel are on the wrong side of the second channel section with respectto the reel onto which the fibre is to be guided. In that case thecutter causes an additional fibre break after the accumulatorwheel/transfer wheel has been moved into the initial position requiredby the changeover. After the break the fibre automatically moves intothe channel, and thus the changeover can be performed as usual.

[0040] The embodiments described above are by no means intended to limitthe invention, but the invention may be modified freely within theclaims. It is thus clear that the apparatus of the invention or itsdetails need not exactly correspond to those shown in the figures, butother solutions are also possible. For example, the second channelsection can also be formed by two belt sections as shown in FIG. 6, etc.In an embodiment like this the controllers at the edges of the belts canbe parts that that turn sideways.

1. A proof testing method for optical fibre where a fibre (1) is guided to a first pulling device (2) and further to a second pulling device (3) and then onto a reel (11, 12), whereby the pulling devices subject the fibre to a desired amount of tensile strength, as a result of which the fibre breaks if the fibre (1) strength is insufficient, characterized in that in the case of a fibre (1 ) break the fibre end is guided between the first and the second pulling device (2, 3) by means of a first channel section (5), which guides the fibre to the second pulling device (3), and that after the second pulling device (3) the fibre end is guided into a second channel section (8) which is off the normal fibre track and along which the fibre (1) is guided into a scrap fibre processing system, and that at a desired moment the fibre (1) is guided from the second channel section (8) to the normal track, along which the fibre is guided onto a reel (11, 12).
 2. A method according to claim 1, characterized in that after a fibre break the fibre (1) is guided onto a different reel than before the fibre break.
 3. A proof testing apparatus for optical fibre, the apparatus comprising a first pulling device (2) and a second pulling device (3) and a winding device, the pulling devices being arranged to subject the fibre to a desired amount of tensile stress which makes the fibre break if the fibre (1) strength is insufficient, characterized in that the apparatus comprises a first channel section (5) which in the case of a fibre (1) break is arranged to guide the fibre end between the first and the second pulling device (2, 3) to the second pulling device (3), a second channel section (8) which is after the second pulling device (3) off the normal fibre track and arranged to guide the fibre into a scrap fibre processing system, and transfer means (7, 9, 10, 31-38) which are arranged to guide the fibre (1) at a desired moment from the second channel section (8) to the normal track, which is arranged to guide the fibre onto a reel (11, 12).
 4. An apparatus according to claim 3, characterized in that after a fibre break the transfer means (7, 9, 10, 31-38) are arranged to guide the fibre (1 ) to a different reel than before the fibre break.
 5. An apparatus according to claim 3, characterized in that the first channel section (5) is formed of a tubular member.
 6. An apparatus according to claim 3, characterized in that the first channel section (5) is arranged to comprise two adjacent belts (23, 24).
 7. An apparatus according to claim 3, characterized in that the second channel section (8) is made of a tubular member which is openable in the longitudinal direction.
 8. An apparatus according to claim 3, characterized in that the second channel section (8) is formed by means of two plate-like members (27, 28) which are close to each other.
 9. An apparatus according to claim 3, characterized in that the second channel section (8) is formed by means of two belts.
 10. An apparatus according to claim 3, characterized in that the first channel section (5) is provided with a cutter (6, 30) for cutting the fibre (1) at a desired moment. 